MySQL 8.0 up up up~
从 MySQL 5.7 开始，支持在线动态调整 innodb buffer pool，并为此新增了一个状态变量 Innodb_buffer_pool_resize_status，可以通过观察它了解调整 buffer pool 过程中的一些状态，例如 Resizing also other hash tables. 或 Completed resizing buffer pool at 230131 15:57:03.。
从 8.0.31 开始，针对 innodb buffer pool 在线动态 resize 特性，新增了下面两个状态变量，可以更方便透明观察 resize 的进度：
我们可以通过 Innodb_buffer_pool_resize_status_code 报告的状态码，了解当前的状态，以及是否出现报错等情况。
状态变量 Innodb_buffer_pool_resize_status_progress 可以实时查看当前 resize 的百分比进度，当有多个 buffer pool instance 时，每完成一个 instance resize，该值就会更新一次。每当 Innodb_buffer_pool_resize_status_code 状态码变化一次，则 progress 的进度百分比会被重置为 0，重新开始。当整个 buffer pool 都 resize 完成后，最终显示 100。
接下来，我们找个正在跑 sysbench 压测中的实例，对其在线调整 buffer pool 看看这几个状态变量分别是怎样的。压测期间，在另一个窗口跑下面的命令观察：
$ while [ 1 ] ; do mysqladmin ext | grep -i Innodb_buffer_pool_resi | sed 's/ //g'; sleep 0.5; echo ; echo; done...|Innodb_buffer_pool_resize_status|bufferpool7:withdrawingblocks.(112590/122869)||Innodb_buffer_pool_resize_status_code|3||Innodb_buffer_pool_resize_status_progress|0|...|Innodb_buffer_pool_resize_status|bufferpool7:resizingwithchunks16to1.||Innodb_buffer_pool_resize_status_code|5||Innodb_buffer_pool_resize_status_progress|87|...|Innodb_buffer_pool_resize_status|Completedresizingbufferpoolat2302029:58:50.||Innodb_buffer_pool_resize_status_code|0||Innodb_buffer_pool_resize_status_progress|100|
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此外，还可以从日志文件中查看详细过程：
09:56:20.275388+08:00 30 .. Resizing buffer pool from 17179869184 to 8589934592 (unit=134217728). (new size: 8589934592 bytes)09:56:20.275397+08:00 0 .. Status code 1: Resizing buffer pool from 17179869184 to 8589934592 (unit=134217728).09:56:20.275417+08:00 0 .. Status code 1: 12% complete09:56:20.275422+08:00 0 .. Status code 1: 25% complete...09:56:20.275439+08:00 0 .. Status code 1: 100% complete09:56:20.275443+08:00 0 .. Status code 1: Completed09:56:20.275446+08:00 0 .. Status code 2: Disabling adaptive hash index.09:56:20.286907+08:00 0 .. disabled adaptive hash index.09:56:20.286939+08:00 0 .. Status code 2: 12% complete09:56:20.286943+08:00 0 .. Status code 2: 25% complete...09:56:20.286963+08:00 0 .. Status code 2: 100% complete09:56:20.286966+08:00 0 .. Status code 2: Completed09:56:20.286970+08:00 0 .. Status code 3: Withdrawing blocks to be shrunken.09:56:20.286974+08:00 0 .. buffer pool 0 : start to withdraw the last 65530 blocks.09:56:20.288848+08:00 0 .. Status code 3: buffer pool 0 : withdrawing blocks. (52526/65530)09:56:20.288865+08:00 0 .. buffer pool 0 : withdrew 52512 blocks from free list. Tried to relocate 14 pages (52526/65530)....09:56:20.288934+08:00 0 .. Status code 3: buffer pool 0 : withdrawing blocks. (52526/65530)09:56:20.288937+08:00 0 .. buffer pool 0 : withdrew 0 blocks from free list. Tried to relocate 0 pages (52526/65530).09:56:20.288941+08:00 0 .. buffer pool 0 : will retry to withdraw later.09:56:20.288951+08:00 0 .. buffer pool 1 : start to withdraw the last 65530 blocks.09:56:20.290815+08:00 0 .. Status code 3: buffer pool 1 : withdrawing blocks. (53263/65530)09:56:20.290824+08:00 0 .. buffer pool 1 : withdrew 53249 blocks from free list. Tried to relocate 14 pages (53263/65530). -- 尝试释放buffer pages失败，将继续重试...09:56:27.305382+08:00 0 .. buffer pool 7 : withdrew 0 blocks from free list. Tried to relocate 0 pages (54852/65530).09:56:27.305385+08:00 0 .. buffer pool 7 : will retry to withdraw later.09:56:27.305388+08:00 0 .. Will retry to withdraw 8 seconds later.09:56:29.047052+08:00 0 .. Page cleaner took 12405ms to flush 83911 and evict 0 pages09:56:35.305806+08:00 0 .. buffer pool 0 : start to withdraw the last 65530 blocks.09:56:35.333782+08:00 0 .. Status code 3: buffer pool 0 : withdrawing blocks. (65530/65530)09:56:35.333813+08:00 0 .. buffer pool 0 : withdrew 0 blocks from free list. Tried to relocate 13004 pages (65530/65530).09:56:35.334245+08:00 0 .. buffer pool 0 : withdrawn target 65530 blocks.09:56:35.334253+08:00 0 .. Status code 3: 12% complete...09:56:35.515813+08:00 0 .. Status code 3: 100% complete09:56:35.515817+08:00 0 .. Status code 3: Completed09:56:35.515821+08:00 0 .. Status code 4: Latching whole of buffer pool.09:56:35.515824+08:00 0 .. Status code 4: 14% complete09:56:35.515827+08:00 0 .. Status code 4: 28% complete09:56:35.515838+08:00 0 .. Status code 4: 42% complete09:56:35.515842+08:00 0 .. Status code 4: 57% complete09:56:35.515845+08:00 0 .. Status code 4: 71% complete09:56:35.515848+08:00 0 .. Status code 4: 85% complete09:56:35.515851+08:00 0 .. Status code 4: 100% complete09:56:35.515862+08:00 0 .. Status code 4: Completed09:56:35.515865+08:00 0 .. Status code 5: Starting pool resize09:56:35.515868+08:00 0 .. Status code 5: buffer pool 0 : resizing with chunks 16 to 8.09:56:35.533458+08:00 0 .. buffer pool 0 : 8 chunks (65530 blocks) were freed.09:56:35.533477+08:00 0 .. Status code 5: 12% complete...09:56:35.639495+08:00 0 .. Status code 5: buffer pool 7 : resizing with chunks 16 to 8.09:56:35.655714+08:00 0 .. buffer pool 7 : 8 chunks (65530 blocks) were freed.09:56:35.655732+08:00 0 .. Status code 5: 100% complete09:56:35.655746+08:00 0 .. Completed to resize buffer pool from 17179869184 to 8589934592.09:56:35.655750+08:00 0 .. Re-enabled adaptive hash index.09:56:35.655755+08:00 0 .. Status code 5: Completed09:56:35.655758+08:00 0 .. Status code 0: Completed resizing buffer pool at 230202 9:56:35.09:56:35.655761+08:00 0 .. Status code 0: 100% complete
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结合上一篇文章 MySQL 8.0不再担心被垃圾SQL搞爆内存，可以看到 MySQL 8.0 在各个细节方面做的是越来越好了。
延伸阅读
Configuring InnoDB Buffer Pool Size, https://dev.mysql.com/doc/refman/8.0/en/innodb-buffer-pool-resize.html
Changes in MySQL 8.0.31, https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-31.html
statvar_Innodb_buffer_pool_resize_status_code, https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html
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